Plasma products produced during CVD, etching and sputtering processing for manufacturing semiconductor devices in a plasma processing apparatus become fixed to an inner wall of a vacuum vessel in the plasma processing apparatus. For example, when silicon nitride (SiN) film is deposited on a sample surface using gases such as SiH.sub.4 gas and N.sub.2 gas or NH.sub.3 gas which react to form SiN, silicon nitride or powdery silicon, which is produced by decomposition of residual SiH.sub.4 becomes fixed or the inner surface of the reaction chamber of the apparatus. Further, when silicon oxide film or silicon nitride film is etched by a CF.sub.4 gas plasma using a mask of photoresist, carbon fluoride caused by ionization decomposition from the gas is bonded with the photoresist and organic resin film is deposited on the inner wall of the vacuum vessel. When the deposited material fixed to the inner wall of the reaction chamber is peeled off, it causes problems in that processing conditions are changed, and the sample is contaminated by the peeled deposit.
It is known to periodically clean the reaction chamber of a plasma processing apparatus in such a manner that the deposit is etched by introducing gas containing a halogen element and generating plasma, or by ashing the deposit using oxygen plasma. It is necessary to generate the plasma near the cleaning portion so that the plasma reaches the portion to be cleaned or to expose ion current to the deposit for cleaning the deposit effectively. In this regard, many kinds of plasma processing apparatuses have been proposed, as follows.
For example, cleaning efficiency is enhanced by changing the incident direction of ions in such a manner that the magnetic field gradient in the reaction chamber is alternately inverted during the processing and cleaning of the reaction chamber, of by forming a cusp magnetic field as shown in FIGS. 3 and 4 of Japanese Patent Laid-Open No. 62-287623, respectively.
The cleaning efficiency of the reaction chamber is enhanced by providing a conductive protection wall at the inner wall of the reaction chamber. The conductive protection wall is able to apply a number of electrical potentials selectively and form divergent radiation of the plasma at the inner wall of the reaction chamber by the method disclosed in FIG. 1 of Japanese Patent Laid-Open No. 1-231320. Further, Japanese Patent Laid-Open No. 63-111177 discloses a method for cleaning effectively the desired portion of a reaction chamber by adjusting the plasma generating position thereby changing the cyclotron resonance point.
The above-mentioned prior art apparatuses have a drawback in that they do not consider how to effectively and uniformly clean the inside of the vacuum vessel and they are not able to effectively and uniformly clean within the vacuum vessel.